* Opposition coalition blames Assad
* Turkey says too early to apportion blame
* Activist blames rebel infighting (Adds comment from SNC President)
By Sinan Abu Mazer
REYHANLI, Turkey, Feb 12 (Reuters) - A deadly minibus blast on Turkey's border with Syria appeared to have targeted a Syrian National Council opposition delegation, the group said on Tuesday, but the Turkish authorities said it was too early to apportion blame.
The minibus, bearing Syrian number plates, exploded at a crossing on the border near the Turkish town of Reyhanli on Monday, opposite the rebel-held Syrian gate of Bab al-Hawa, killing 14 people and wounding dozens more.
"We entered Syria from Turkey through Bab al-Hawa. Had we been there 30 minutes earlier we would have been the targets," said George Sabra, president of the Syrian National Council (SNC), an opposition group in exile.
"After crossing the border we heard the explosion but we continued on our way," he told a news conference in Istanbul.
Sabra said he and other SNC members were returning from a trip in northern Syria, including Aleppo, Idlib and Azaz, to assess the latest situation on the ground in rebel-held areas.
The SNC said earlier in a statement that "Syrian regime tools" carried out the bombing.
"We have enough experience of the regime. We know its fingers are everywhere and yesterday they were in Bab al-Hawa," Sabra said when asked if he had specific intelligence on who was responsible for the explosion.
Turkish police investigations were focusing on three people seen leaving the minibus before the explosion, officials said.
"This is a terrorist act. We are working on several alternatives. It was probably carried out by a Syrian," Turkish Interior Minister Muammer Guler told reporters in parliament.
The minibus was parked in a waiting area at the Cilvegozu border post, one of the main crossing points for humanitarian aid into Syria, when it exploded, according to Turkey's Deputy Prime Minister Besir Atalay.
"Amid the bustle, a Syrian-plated vehicle arrives, waits for some time and three people slip away. Twenty minutes later the vehicle exploded," the minister said.
"There is footage and prosecutors and police are working on that," he said, declining to speculate on who was responsible.
Two of the three people left in a car heading into Syria and the third person slipped away into Turkey, media reports said.
One activist said the blast could have been the work of one of several factions within Syria's armed opposition coalition, including the al Qaeda-linked Jabhat al-Nusra, one of the most coherent and disciplined anti-Assad forces in Syria.
Turkey's interior, justice and customs ministers flew to the area late on Monday to be briefed on the incident.
The customs minister told a news conference security would be increased at the border but humanitarian aid would continue to be sent across, state-run Anatolian news agency reported.
At least 28 people were wounded in the attack. The blast also damaged scores of vehicles at the border post, where a gate was blown open and part of the roof collapsed.
Turkey is a staunch supporter of the near two-year uprising against Assad and has harboured both Syrian refugees and rebels. Violence has sometimes spilled over the border.
Tensions increased in recent weeks after NATO said it had detected launches of short-range ballistic missiles inside Syria, several of which have landed close to the Turkish border. Turkey has scrambled war planes along the frontier, fanning fears the war could spread and further destabilise the region. (Additional reporting by Can Sezer in Istanbul, Orhan Coskun in Ankara, Khaled Yacoub Oweis in Amman; Writing by Daren Butler; Editing by Nick Tattersall and Jon Hemming)